Ferry companies have done much to clean up their act in terms of waste disposal and engine pollution, and the sheer numbers of passengers on a conventional cross-channel ferry mean that emissions per person will be low, and as many piggy back on freight services your actual carbon footprint is likely to be minimal. A standard car ferry emits just 10kg of CO2 per foot passenger for a return trip Dover-Calais. High-speed ferries, such as the catamarans that travel out to the Channel Islands, use engines with a much higher carbon count, but compared with short-haul flying even they are likely to come up greener as their emissions aren't at high altitude where CO2 exerts a greater effect on the environment. You can now offset emissions for most UK ferry routes via a new online ferry booking service, ferrygreen.com.